1. Field of the Invention
The present invention relates to a light emission device which can be used as a light source for a display device.
2. Description of Related Art
A liquid crystal display device (LCD) is a non-self emissive display device. The LCD includes a liquid crystal (LC) panel assembly and a backlight unit for emitting light toward the LC panel assembly. The LC panel assembly receives light emitted from the backlight unit and selectively transmits or blocks the light using a liquid crystal layer.
The backlight unit is classified, according to a light source, into different types, one of which is a cold cathode fluorescent lamp (CCFL). The CCFL is a linear light source that can uniformly emit light to the LC panel assembly through a plurality of optical members such as a diffusion sheet, a diffuser plate, and/or a prism sheet.
However, since the CCFL emits the light through the optical members, there may be a light loss. In the CCFL type LCD, only 3-5% of light generated from the CCFL is transmitted through the LC panel assembly. Furthermore, since the CCFL has relatively higher power consumption, the overall power consumption of the LCD employing the CCFL increases. In addition, since the CCFL is difficult to be large-sized due to its structural limitation, it is hard to apply CCFL to a large-sized LCD over 30-inch.
A backlight unit employing light emission diodes (LEDs) is also well known. The LEDs are point light sources that are combined with a plurality of optical members such as a reflection sheet, a light guiding plate, a diffusion sheet, a diffuser plate, a prism sheet, and/or the like, thereby forming the backlight unit. The LED type backlight unit has fast response time and good color reproduction. However, the LED is costly and increases an overall thickness of the LCD.
The conventional backlight units are driven so as to maintain a predetermined brightness all over the light emission surface when the LCD is driven. Therefore, it is difficult to improve the display quality to a sufficient level.
For example, when the LC panel assembly intends to display an image having a high luminance portion and a low luminance portion in response to an image signal, it will be possible to realize an image having a more improved dynamic contrast if the backlight unit can emit lights having different intensities to pixels of the LC panel assembly displaying the high and low luminance portions.
However, the conventional backlight units cannot achieve the above function and thus there is a limitation in improving the dynamic contrast of the image displayed by the LCD.